1. Field of the Invention
The present invention relates to an ink ejecting device of an ink-jet printer, and in particular relates to a piezoelectric element of the ink ejecting device.
2. Description of Related Arts
A conventional ink ejecting device of an ink-jet printer includes a ceramic cavity plate that includes ink chambers, which are divided by separation walls, and a piezoelectric element attached to the cavity plate. In such an ink ejecting device, the piezoelectric element induces a pressure change within the ink chambers, which forces the ejection of ink from the ink chambers through nozzles provided on the cavity plate.
Various kinds of piezoelectric elements have been applied to the conventional ink ejecting device; one of which is a laminated piezoelectric element. This type of piezoelectric element has a layer structure of sheet-shaped piezoelectric materials, on which positive and negative electrode patterns are alternately created at regular intervals by screen process printing. Multiple grooves are formed on the piezoelectric element so as to detach deforming portions respectively after the removal of a binder and the sintering process. Each deforming portion is positioned above one of the ink chambers, whereby the piezoelectric element appropriately forces the ejection of ink from each ink chamber.
However, the piezoelectric element shrinks during the sintering process. This shrinkage often causes slippage of the layer structure or uneven intervals between the electrode patterns. As a result, the ink ejecting performance varies from nozzle to nozzle even in the same ink ejecting device, since the ability to distort a piezoelectric element is not uniform. Conventionally, the voltage or the waveform of signals supplied to the piezoelectric element is adjusted on each nozzle in order to regulate the ink ejecting performance, although this complicates the control of such an ink ejecting device.
In order to solve the problem mentioned above, the object of the invention is therefore to provide an ink ejecting device which has a uniform ink ejecting performance for each nozzle without intricate control thereof. The ink ejecting device of the invention comprises ink chambers, provided at regular intervals on a cavity plate, that store ink, and a piezoelectric element attached to the cavity plate. A pressure change is caused within the ink chamber by the piezoelectric element in this ink ejecting device, thereby, forcing the ejection of ink through nozzles.
According to the invention, the piezoelectric element is made of: piezoelectric materials; discrete electrodes provided above the ink chamber or above a separation wall on each of the piezoelectric materials; and an electrode, common to all the ink chambers, that operates as an outer layer covering the outside of the piezoelectric materials. Particularly, the piezoelectric element defines a cut in the common electrode to equalize the ink ejecting velocity of each nozzle.
With this arrangement, the cut in the common electrode creates an area where an electric field is not induced in the piezoelectric element, when applying a voltage to the electrodes. The extent of deformation of the piezoelectric element is reduced in this area, which decreases the ink ejecting velocity. In other words, it is possible to regulate the ink ejecting performance by providing the cut, thereby, adjusting the extent of deformation so that the ink ejecting velocity is equalized on each nozzle. This guarantees good image forming performance, even if the piezoelectric element shrinks during the sintering process.
Further, the cut in the common electrode is provided above the center of the ink chamber so that the deforming portion and the non-deforming portion of the piezoelectric element are well balanced. The ink ejecting velocity is appropriately regulated in this configuration.
Still further, the size of the cut is in proportion to the deceleration of the ink ejecting velocity. The size of the cut can be immediately determined when measuring the ink ejecting velocity, which realizes the prompt adjustment of ink ejecting performance.
In the aforementioned configuration, the common electrode may preferably cause the piezoelectric element to deform in unimorph mode. In this case, the common electrode is provided so as to cover the outer surface of the piezoelectric materials and to be exposed to the exterior. Therefore, it is easy to create the cut on the common electrode, and therefore at the same time, easy to adjust the ink ejecting velocity. Alternately, the common electrode may preferably cause the piezoelectric element to deform in bimorph mode. The extent of deformation in unimorph mode or in bimorph mode can be adjusted by providing the cut on the common electrode. As noted above, the cut in the common electrode creates the area where an electric field is not induced. The extent of deformation is reduced in total, because the deformation in both of unimorph mode and bimorph mode does not occur in this area. This phenomenon is utilized to regulate the ink ejecting velocity, according to the invention.
Another aspect of the invention is to provide a piezoelectric element for the aforementioned ink ejecting device that has a uniform ink ejecting performance. Again, the piezoelectric element is made of: piezoelectric materials; discrete electrodes that provide multiple deforming portions on the piezoelectric materials; and an electrode common to all the deforming portions, covering the outer surface of the piezoelectric materials so as to be exposed to the exterior. The piezoelectric element also defines the cut in the common electrode that is provided to equalize the extent of deformation. The cut creates the area where an electric field is not induced in the piezoelectric element, thereby not causing deformation partially. It is thus possible to regulate the extent of deformation by providing the cut in the common electrode.